Collaborative project: CSEDI -Understanding Si and Fe differentiation in Earth's mantle and core through experimental and theoretical research in geochemistry and mineral physics

合作项目：CSEDI - 通过地球化学和矿物物理的实验和理论研究了解地幔和地核中的硅和铁分异

• 批准号: 1502591
• 负责人: Nicolas Dauphas
• 金额: $ 23.63万
• 依托单位: University of Chicago
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-04-15 至 2018-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1502591&HistoricalAwards=false
• 关键词: Collaborative; project; CSEDI; Understanding; Si

To first order, the Earth is divided into three concentric shells of different nature: the metallic core, the rocky mantle, and the fluid atmosphere/hydrosphere. While samples are available from the mantle and atmosphere/hydrosphere, the nature and composition of the core remain poorly understood. In particular, the core is known to be less dense than pure iron-nickel alloy, indicating that another light element is present in the core, possibly oxygen, silicium, or sulfur. The conditions (pressure and temperature) under which Earth's core formed and the nature of the light element in Earth's core are two major unresolved questions in planetary sciences. Because no core samples are directly available for study, scientists rely on remote seismic observations or other indirect methods to address those questions. In the proposed work, the approaches of geochemistry (the chemistry of the Earth), mineral physics (solid state physics applied to natural materials), and computational techniques will be combined to set limits on the temperature condition during core formation and the nature of the light element in Earth's core. This will be achieved by examining the extent to which different isotopic flavors of silicon and iron were partitioned between metal and silicate when the core formed. The work will involve synthesizing minerals in the laboratory and compressing them to pressure conditions relevant to the deep Earth by confining the samples between two diamonds, measuring the strength of the iron bonds in those minerals at a synchrotron source that produces very energetic X-rays, and examining, through computer calculations, the behavior of matter under high pressure and temperature. This work can impact many fields of science, ranging from the origin of Earth's dynamo to characterization of extrasolar planets through measurement of their mass. All PIs will actively engage in training and educating graduate students, undergraduate students, and postdocs in the proposed research projects. The PIs will continue developing SciPhon, a user-friendly, free software for NRIXS data reduction. This program will be made available to various communities studying different aspects of NRIXS, including geochemistry, mineral physics, material sciences, condensed matter physics, and biochemistry. All PIs will be actively involved in outreach programs including the UTeach Outreach Program that conducts academic summer camps for underrepresented K-12 kids from the Austin and southwest Texas area. The mass of the Earth and its accretion history are such that core-mantle differentiation was probably unavoidable but considerable uncertainties remain as to how and when this took place. Our limited understanding of this major event arises from our lack of sampling of Earth's deep interior. Scientists have devised indirect approaches to address this shortcoming by relying on (1) mineral physics experiments to reproduce the high pressure-temperature conditions prevailing in Earth's interior, (2) theoretical calculations to mimic those same conditions, and (3) geochemical measurements of the composition of mantle rocks to search for telltale signatures of core formation. These strongly interweaved approaches have led to significant progress but first-order unanswered questions remain, such as under what pressure-temperature conditions did the core form, what is the nature of the light element in the core, and did core formation fractionate Si and Fe isotopes. Terrestrial basalts have non-chondritic Si and Fe isotopic compositions, which could reflect partitioning of these elements into the core, although other interpretations exist. The investigators propose to establish Si and Fe isotope fractionation factors using high-pressure nuclear resonant inelastic X-ray scattering (NRIXS) and theoretical calculations at deep mantle conditions via collaborative approaches in geochemistry (Dauphas), theoretical ab initio calculations (Wentzcovitch), and experimental mineral physics (Lin). The derived force constants of Si and Fe bonds in basaltic glasses, lower-mantle minerals (bridgmanite and ferropericlase), and Fe alloys will allow us to build a deep-Earth geochemical model to evaluate if the specific Si and Fe isotopic compositions of the silicate Earth reflect core partitioning, and if they do, put constraints on important aspects of core formation such as temperature or the presence of Si as a light element in the core. The experimental results will serve as a benchmark for ab initio calculations of Si and Fe isotopic fractionation between relevant metal and silicate phases at high pressure and temperature. The theoretical work will in turn guide and refine the experimental and geochemical modelling efforts, focusing in particular on nuclear resonant measurements, force constant derivations, anharmonic and spin crossover effects. The exchanges and feedbacks between geochemists and experimental and theoretical physicists involved in this project will provide a holistic view of Si and Fe isotopic fractionation during core formation.

首先，将地球分为三个不同性质的同心壳：金属芯，岩石地幔和流体气氛/水圈。虽然可以从地幔和大气/水圈中获得样品，但核心的性质和组成仍然很少理解。特别是，已知芯比纯铁 - 尼克合金密集，表明核心中存在另一个光元素，可能是氧气，硅或硫。地球核心形成的条件（压力和温度）以及地球核心中光元的性质是行星科学中的两个主要未解决的问题。由于没有直接可用于研究的核心样本，因此科学家依靠远程地震观察或其他间接方法来解决这些问题。在拟议的工作中，地球化学方法（地球的化学），矿物质物理学（应用于天然材料的固态物理学）和计算技术将合并以在核心形成过程中对温度条件和地球核心光元素的性质设定限制。这将通过检查核心形成时在金属和硅酸盐之间分配的不同同位素风味的程度来实现这一点。这项工作将涉及实验室中的矿物质合成，并通过限制两颗钻石之间的样品来压缩与深层的压力条件，从而在同步子源中测量这些矿物质中铁键的强度，从而产生非常有力的X射线，并通过计算机计算，高压和温度的行为，从而产生非常有力的X射线。这项工作可能会影响许多科学领域，从地球发电机的起源到通过测量质量来表征地球外行星的表征。 所有PI都将积极从事培训和教育研究生，本科生以及拟议研究项目的博士后。 PI将继续开发Sciphon，这是一种用于NRIXS数据减少的用户友好的免费软件。该计划将提供给研究NRIX各个方面的各个社区，包括地球化学，矿物质物理学，材料科学，冷凝物质物理学和生物化学。 所有PI都将积极参与外展计划，包括UTEACH外展计划，该计划为来自奥斯汀和西南德克萨斯州地区的代表性不足的K-12儿童进行学术夏令营。 地球的质量及其积聚历史使得核心掩饰的分化可能不可避免，但对于如何以及何时发生的情况仍然存在。我们对这一重大事件的有限理解是由于我们缺乏对地球深层内部的取样。 Scientists have devised indirect approaches to address this shortcoming by relying on (1) mineral physics experiments to reproduce the high pressure-temperature conditions prevailing in Earth's interior, (2) theoretical calculations to mimic those same conditions, and (3) geochemical measurements of the composition of mantle rocks to search for telltale signatures of core formation.这些牢固的交织方法导致了重大进展，但仍然存在一阶未解决的问题，例如在核心形式的压力温度条件下，核心中光元的性质是什么，并且核心形成分数Si和Fe同位素。陆生玄武岩具有非基质Si和Fe同位素组成，尽管存在其他解释，但可以反映这些元素将这些元素分配到核心中。研究人员建议通过高压核共振非弹性X射线散射（NRIXS）和理论计算在深壁炉条件下通过地球化学方法（DAUPHAS），理论Ab Ab Initio Absible计算（Wentzcovitch）（Wentzcovitch）和实验性矿物质物理（LIN）来建立SI和FE同位素分馏因子。 The derived force constants of Si and Fe bonds in basaltic glasses, lower-mantle minerals (bridgmanite and ferropericlase), and Fe alloys will allow us to build a deep-Earth geochemical model to evaluate if the specific Si and Fe isotopic compositions of the silicate Earth reflect core partitioning, and if they do, put constraints on important aspects of core formation such as temperature or the presence of Si as a核心中的轻元素。实验结果将作为在高压和温度下相关金属和硅酸盐阶段之间的Si和Fe同位素分馏的从头算的基准。理论工作反过来将指南并完善实验和地球化学建模工作，尤其集中于核共振测量，力量恒定推导，非谐波和自旋交叉效应。地球化学主义者与参与该项目的实验物理学家之间的交流和反馈将提供对核心形成过程中Si和Fe同位素分馏的整体视图。